The present invention relates generally to methods and systems for measuring physical properties of materials, and more particularly to a direct measurement system for determining the complex moduli of polymeric materials.
Methods for measuring complex moduli of polymeric damping materials generally are of two major types, namely, indirect resonant beam techniques and direct stiffness systems. The beam techniques are considered to be indirect because complex modulus values for the polymeric material are calculated, using appropriate formulae, from measurements of changes in modal damping and resonant frequency occurring in a beam of the polymeric material or in a beam coated with a polymer layer. Errors may arise because small differences between measurements on coated and uncoated beams may be magnified because of assumptions made in the mathematical treatment.
Direct measurement systems operate by applying an appropriate time varying force to a specimen of the polymeric material and calculating the complex modulus from a measured response to that force. The measurement chain is often quite long and consists of many finite mass and stiffness elements which are major sources of error, such as unwanted resonances in the desired frequency range or systematic under-estimation of true specimen stiffness when near the system stiffness. These disadvantages are difficult to overcome and direct stiffness measurement systems are best used for low to medium range measured modulus values.
The invention solves or substantially reduces in critical importance problems with prior art systems and methods as just described by providing system and method for measuring complex shear or Young's modulus of a polymeric material wherein first ends of two parallel beams of unequal thicknesses are attached to a base with a polymer specimen between the second ends, a time varying force is applied to one beam and the displacement responses of both beams are measured, with amplitude and phase angles determined by suitable displacement measuring sensors. The complex modulus of the polymer at the specific driving frequency and temperature is determined using an equation.
It is therefore a principal object of the invention to provide improved system and method for measuring physical properties of materials.
It is a further object of the invention to provide system and method for direct measurement of complex moduli of polymeric materials.
It is yet another object of the invention to provide system and method for direct measurement of shear or Young's modulus of polymeric materials over wide frequency and temperature ranges.
These and other objects of the invention will become apparent as a detailed description of representative embodiments proceeds.